Subgrade vaults are widely used where circuits from major access lines branch off to distribution lines. Examples exist where distribution lines depart from a major access lines to serve an individual house. Other vaults might serve a part of a drainage or a water supply system, and can provide a chamber for valves, switches and connections.
These vaults have in common a peripheral wall, an open bottom and a top access port. The peripheral wall is provided with openings to pass the lines.
A cover is provided that seats on the vault to close the access port It is made strong enough to support anticipated static and dynamic loads that may be exerted on it by persons or vehicles. Importantly, the cover must reliably close the access port and be firmly and reliably in place when not attended.
While this as an obvious requirement, its observation is sometimes uncertain. These vaults are installed with the access port at or beneath grade, and frequently are below drainage water levels. They are intended to blend into their surroundings. Often the color of the vault and cover approach the color of a surrounding lawn or golf course, and their presence or absence is often not noticed.
The preferred material of construction for the vault and cover is high density polyethylene which has a specific gravity of about 0.95. If desired, additives such as glass fibers can be mixed into the resin. Also, materials other than resins can be sued for the structures, cementitious material for example. While as a practical matter a vault or cover of this material is not especially buoyant, neither does it because of its weight and specific gravity exert much resistance to a sufficient force of water. An unrestrained cover atop a rising flow of water, or a partially raised cover in the path of a swift flow of water, can readily be displaced and perhaps carried away. In either event, the open access port is unlikely to be visible, and a person or vehicle can unwittingly step or fall into it and be injured.
It is an object of this invention to provide a vault with a cover that can readily and reliably be attached to the vault to close the access port. The exertions required for this purpose are those which are general behavior, requiring no tool and no special observance of a procedure. Merely stepping on the cover will do the job.
Another important feature is the ready removal of the cover to open the access port for service. A common tool carried by every maintenance person will suffice, although a specific type of the tool is needed. The unlatching operation is a simple one-handed task, but the cover will not be released unless the exertion is properly done.
A further advantage of this vault and cover is that the entire latching mechanism except for a protruding latch pin is entirely within the envelope of the cover.